brain
Americannoun
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brains
plural
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Anatomy, Zoology. the part of the central nervous system enclosed in the cranium of humans and other vertebrates, consisting of a soft, convoluted mass of gray and white matter and serving to control and coordinate the mental and physical actions.
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Zoology. (in many invertebrates) a part of the nervous system more or less corresponding to the brain of vertebrates.
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(used with a plural verb) Sometimes brains. understanding; intellectual power; intelligence.
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the brain as the center of thought, understanding, etc.; mind; intellect.
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Slang. brains, a member of a group who is regarded as its intellectual leader or planner.
The junior partner is the brains of the firm.
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Informal. a very intelligent or brilliant person.
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Informal.
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the controlling or guiding mechanism in a computer, robot, pacemaker, etc.
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the part of a computer system for coordination or guidance, as of a missile.
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verb (used with object)
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brains,
present (3rd person singular)
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brained,
past participle, past
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braining
present participle
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to smash the skull of.
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Slang. to hit or bang (someone) on the head.
idioms
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beat one's brains out, to try very hard to understand and work out a problem, remember something, etc..
She beat her brains out studying for the exam.
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have something on the brain, to have an obsession; be occupied with.
Lately I seem to have food on the brain.
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pick someone's brains, to obtain information by questioning another person rather than by seeking it independently.
He refused to prepare for the exam but counted on being able to pick his roommate's brains.
noun
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Technical name: encephalon. the soft convoluted mass of nervous tissue within the skull of vertebrates that is the controlling and coordinating centre of the nervous system and the seat of thought, memory, and emotion. It includes the cerebrum, brainstem, and cerebellum
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the main neural bundle or ganglion of certain invertebrates
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informal (often plural) intellectual ability
he's got brains
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informal shrewdness or cunning
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informal an intellectual or intelligent person
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informal (usually plural; functioning as singular) a person who plans and organizes an undertaking or is in overall control of an organization, etc
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an electronic device, such as a computer, that performs apparently similar functions to the human brain
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constantly in mind
I had that song on the brain
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to obtain information or ideas from someone
verb
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to smash the skull of
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slang to hit hard on the head
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The part of the nervous system in vertebrates that is enclosed within the skull, is connected with the spinal cord, and is composed of gray matter and white matter. It is the control center of the central nervous system, receiving sensory impulses from the rest of the body and transmitting motor impulses for the regulation of voluntary movement. The brain also contains the centers of consciousness, thought, language, memory, and emotion.
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See more at brainstem cerebellum cerebrum
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A bundle of nerves in many invertebrate animals that is similar to the vertebrate brain in function and position.
Usage
What is a basic definition of brain? The brain is the organ in humans and animals that’s responsible for thought processes. The plural form brains refers to intelligence or a person who is the smartest member of a group. The word brain has several other senses as a noun and a few as a verb. Your brain is a squishy organ located inside your head and is protected by your skull. The brain is highly complex. It is the seat of all your conscious thoughts and unconscious impulses and is like the control center of the body, allowing you to do things like speak, move your muscles, and breathe without thinking. The brain, spinal cord, and nerves make up the nervous system. Real-life examples: You and every other person have a brain. Animals have brains too, although they aren’t capable of doing all of the things the human brain is able to do. Your brain is very important and has a vast number of jobs, such as keeping all of your memories, telling your other organs what to do, and helping you read these words. Used in a sentence The brain is the most complex and perhaps the most studied organ. The plural form brains is used as a term for intelligence or intellect. This usage alludes to the brain being the organ that handles thinking. Real-life examples: You may have heard a person being described as having brains. This means they are smart and able to figure things out, especially difficult or complex problems. Used in a sentence: I have to study hard to do well in math, but my sister has brains and aces her tests without studying. Relatedly, a person who is considered very smart can be called a brain. Used in a sentence: None of us could figure out the computer problem so we called in Mike, who was a real brain when it comes to fixing them. Brains is also used to refer to the smartest member or members of a group or team, especially the one who comes up with plans. Real-life examples: Movies and shows that feature a heist or a plan often have a person who is referred to as the “brains of the operation.” For example, scientist Bruce Banner often comes up with plans or solutions for the Avengers (when he isn’t getting angry and turning into the Incredible Hulk). In the Harry Potter series, Hermione is definitely the brains of the trio that she forms with Harry and Ron. Used in a sentence: Everyone knew that Edd was the real brains behind the money-making schemes.
Synonym Usage
See mind.
Other Word Forms
Derived Forms
Inflected Forms
Nouns
Participles
Conjugated Forms
Present
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brainsimple
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brainssimple
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have brainedperfect
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has brainedperfect
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am brainingprogressive
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are brainingprogressive
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is brainingprogressive
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have been brainingperfect progressive
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has been brainingperfect progressive
Past
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brainedsimple
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had brainedperfect
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was brainingprogressive
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were brainingprogressive
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had been brainingperfect progressive
Future
Etymology
Origin of brain
First recorded before 1000; Middle English; Old English bræg(e)n, bregen; cognate with Low German brägen, Dutch brein; akin to Greek brégma; see bregma ( def. )
Explanation
The brain is the most complex organ in the body, located inside the protective skull. The word can also be used as a verb in the phrase "to brain," which means to injure or kill someone by hitting them in the head. The human brain has inspired many idioms, or colorful phrases. Thinking intently (or obsessively) about something means that you've got it "on the brain," and to "pick someone's brain" means to get their ideas on something. A puzzle is a "brainteaser, someone smart is called "a brain," and the person who runs something is said to be "the brains" of the operation.
Vocabulary lists containing brain
Common Five-letter Words for Wordle, List 3
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Human Anatomy and Physiology - Introductory
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Human Anatomy and Physiology - High School
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
A severe measles case can cause pneumonia; encephalitis, or dangerous inflammation of the brain; hospitalization; and sometimes death.
From Los Angeles Times ● Aug. 6, 2026
The Food and Drug Administration on Wednesday approved Takeda Pharmaceutical’s 4502 2.96%increase; up pointing triangle Orzeyful, the first medication to treat narcolepsy by targeting a brain chemical that regulates wakefulness.
From The Wall Street Journal ● Aug. 6, 2026
It rattles against the hard edges of your brain until it gets polished and smooth.
From Salon ● Aug. 6, 2026
"Focusing on vascular and metabolic risk factors can still help reduce the combined effects of several brain changes that occur simultaneously," he concludes.
From Science Daily ● Aug. 6, 2026
The brain stem keeps many of your automatic functions going, like your breathing and heartbeat.
From "Phineas Gage" by John Fleischman
When we imagine, for example, those questions we can no longer ask a loved one who has died, such queries, Ms. Watson suggests, help “our brains to process loss, our minds to fathom the unfathomable.”
From The Wall Street Journal ● Aug. 4, 2026
One of the best things about being MarketWatch’s Smart Spending reporter is that I get to pick the brains of top personal-finance experts every day.
From MarketWatch ● Aug. 4, 2026
Yet there is, to date, little evidence-based guidance on effective interventions for kids whose brains work differently.
From Los Angeles Times ● Jul. 24, 2026
The team plan to run workshops and structured interviews with at least 45 anglers to pick their brains about the local ecology and size of sharks caught in the past.
From BBC ● Jul. 19, 2026
Broca notices that in the brains of stroke patients who'd lost the power to speak there is visible damage in a small area on the outside of the left frontal lobe.
From "Phineas Gage" by John Fleischman
They found that the larger brained primate species did not solve the fruit-finding puzzle more efficiently than smaller brained mammals.
From Science Daily ● May 28, 2024
Clevinger, his long hair brained into pigtails, allowed three runs, two earned, and six hits in 4 1/3 innings while striking out six and walking two.
From Seattle Times ● May 10, 2022
At least there’s nothing pointy on the Steam Deck, unlike some of the book corners I’ve brained myself with over the years.
From The Verge ● Mar. 29, 2022
A second major find, the nearly complete skull of a larger brained hominid, long known simply by its field number “1470” and now classified as H. rudolfensis, bolstered that point.
From Science Magazine ● Jan. 2, 2022
No, it was meant to determine if you were right brained or left brained, usually connoted by handedness.
From "Nine, Ten: A September 11 Story" by Nora Raleigh Baskin
We are a long way here from Thor developing the wheel or the Fat Broad braining the Snake.
From Time Magazine Archive
At times, an invisible finger tapped at the panes; it was some bird of the night, drawn by the light, braining itself against the glass….
From Letters from my Windmill by Daudet, Alphonse
"Théo is at home—he went to tell his mother," Joyselle said, nearly braining an old lady with his violin-case as he swung round to speak.
From The Halo by Justice, B. Martin
They succeed; but not without difficulty, and a free handling of handspikes—almost braining the apes before they consent to relinquish it.
From The Flag of Distress A Story of the South Sea by Reid, Mayne
"I guess that was nigh braining the child," quoth Miss Amanda, with the greatest coolness, and without making the least apology.
From Roughing It in the Bush by Moodie, Susanna
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
